1. Field of the Invention
The present invention relates to a heat-sensitive recording material, more particularly, to a heat-sensitive recording material of full-color including a support and at least three heat-sensitive recording layers on the support, the heat-sensitive recording material being excellent in image stability, handling property, color development and fixing speed.
2. Description of the Related Art
Heat-sensitive recording progressed recently since the recording apparatus thereof is simple, reliability is high and maintenance is not necessary. As materials thereof, there are conventionally widely known those utilizing a reaction of an electron-donating colorless dye with an electron-accepting compound which allows the dye to develop color, those utilizing a reaction of a diazo compound or diazonium salt (hereinafter, simply referred to as diazo compound or the like, in some cases) with a coupler which allows this to develop color, and other materials.
Recently, progress of full-color heat-sensitive recording materials is remarkable, and such full-color heat-sensitive recording materials have a structure in which layers that develops yellow, magenta and cyan colors respectively are provided, and full-color images can be formed by heating the layers to cause color development.
As the above-mentioned full-color heat-sensitive recording material, general are materials including a combination of a color-development layer (heat-sensitive recording layer) composed of an electron-donating colorless dye and an electron-accepting compound with a color-development layer composed of a diazo compound or the like and a coupler, in which a yellow layer, magenta layer and cyan layer are provided in this order from the upper layer side.
With the full-color heat-sensitive recording material having the above-mentioned structure, an image is formed. Then the image is fixed by irradiation with light to enhance the stability of the image, by utilizing a photodecomposition property of the diazo compound or the like. In such a light-fixing type full-color heat-sensitive recording material, a layer composed of an electron-donating colorless dye that develops cyan color and an electron-accepting compound is often provided at the lowest layer (layer nearest to a support), for effecting the above-mentioned light-fixation efficiently. However, even in the full-color heat-sensitive recording material of light-fixation type having such a structure, there is a requirement for further improvement in image stability.
Further, improvement in color-developing property is also a great object for the above-mentioned full-color heat-sensitive recording material. However, the above-mentioned full-color heat-sensitive recording material utilizing a reaction of an electron-donating colorless dye with an electron-accepting compound has a problem in image stability since the reaction is an equilibrium reaction, and additionally, there is a necessity to make the content of an electron-accepting compound higher than that of an electron-donating colorless dye. Consequently, a color-development layer containing the above-mentioned electron-donating colorless dye or the like becomes thicker as compared with a color-development layer containing the above-mentioned diazo compound or the like. The thickness of such a color-development layer leads to increased thickness of a full-color heat-sensitive recording material, influencing the color-developing property.
Moreover, since the above-mentioned electron-donating colorless dye and electron-accepting compound is solid-dispersed in a color-development layer, a heat-sensitive recording material is curled by phase transition of them caused by heating, leading to decrease in handling property.
Furthermore, a full-color heat-sensitive recording material including a layer that develops yellow color placed as the uppermost layer has poor fixing speed since the transmittance of light necessary for light-fixation of a diazo compound or the like decreases due to the influence of yellow.
An object of the present invention is to provide a full-color heat-sensitive recording material excellent in image stability, handling property, color development and fixing speed, in view of the above-mentioned problems.
A means for attaining the above-mentioned object is as described below. Namely, the present invention provides a full-color heat-sensitive recording material including a support, and at least a heat-sensitive recording layer that color-develops to yellow color; a heat-sensitive recording layer that color-develops to cyan color and a heat-sensitive recording layer that color-develops to magenta color, sequentially provided on the support in this order from the support side, wherein all of the above-mentioned heat-sensitive recording layers contain a diazo compound and/or diazonium salt; and a coupler compound that reacts with the above-mentioned diazo compound and/or diazonium salt to cause color development.
One aspect of the present invention provides the above-mentioned full-color heat-sensitive recording material, wherein the above-mentioned heat-sensitive recording layer that color-develops to yellow color contains a diazo compound of the following general formula (I):
General Formula (I) 
In the general formula (I), R1, R2, R3 and R4 each independently represent any group selected from the group consisting of a hydrogen atom, halogen atoms, alkyl groups, aryl groups, xe2x80x94OR51, xe2x80x94SR51, xe2x80x94COOR51, xe2x80x94CONR51R52, xe2x80x94SO2R51, xe2x80x94SO2NR51, R52, xe2x80x94COR51, xe2x80x94NR51R52, nitro group and cyano group. R51 and R52 each independently represent any group selected from the group consisting of a hydrogen atom, alkyl groups, aryl groups and acyl group. R5 represents any group selected from the group consisting of a hydrogen atom, alkyl groups, aryl groups, xe2x80x94COOR53, xe2x80x94CONR53R54, xe2x80x94SO2NR53, xe2x80x94SO2NR53R54 and xe2x80x94COR53. R53 and R54 each independently represent any group selected from the group consisting of a hydrogen atom, alkyl groups, aryl groups and acyl group.
Another aspect of the present invention provides the above-mentioned full-color heat-sensitive recording material, wherein the above-mentioned heat-sensitive recording layer that color-develops to cyan color contains at least one of diazonium salts of the following general formulae (A) to (C): 
In the general formula (A), Ar represents a substituted or unsubstituted aryl group. R17 and R18 each independently represent a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group and may be the same and may be different from each other. In the general formula (B), R20, R21 and R22 each independently represent a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group and may be the same and may be different from each other. Y represents a hydrogen atom or OR19. R19 represents a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group. In the general formula (C), R23 and R24 each independently represent a substituted or unsubstituted alkyl group or a substituted or unsubstituted aryl group and may be the same and may be different from each other.
Another aspect of the present invention provides the above-mentioned full-color heat-sensitive recording material, wherein the above-mentioned heat-sensitive recording layer that color-develops to magenta color contains a diazonium salt of the following general formula (1): 
In the general formula (1), R31 and R32 each independently represent a hydrogen atom, alkyl group or aryl group. R33 and R34 each independently represent a hydrogen atom, alkyl group, aryl group or halogen atom. R35, R36, R37, R38 and R39 each independently represent a hydrogen atom, alkyl group, aryl group, halogen atom, alkoxy group, aryloxy group, alkoxycarbonyl group, acyloxy group, carbamoyl group, amide group, cyano group, alkylthio group, arylthio group, alkylsulfonyl group, or arylsulfonyl group. At least one of R35, R36, R37, R38 and R39 represents a halogen atom. Xxe2x88x92 represents an anion.
Further, another aspect of the present invention provides the above-mentioned full-color heat-sensitive recording material, wherein the above-mentioned heat-sensitive recording layer that color-develops to yellow color contains a diazo compound of the above-described general formula (I), the above-mentioned heat-sensitive recording layer that color-develops to cyan color contains at least one of diazonium salts of the above-described general formulae (A) to (C), and the above-mentioned heat-sensitive recording layer that color-develops to magenta color contains a diazonium salt of the above-described general formula (I).
The heat-sensitive recording material of the present invention is characterized in that it includes a support, and at least a heat-sensitive recording layer that color-develops to yellow color, a heat-sensitive recording layer that color-develops to cyan color and a heat-sensitive recording layer that color-develops to magenta color, on the support in this order from the support side. All of the above-mentioned heat-sensitive recording layers contain a diazo compound and/or diazonium salt and a coupler compound that reacts with the above-mentioned diazo compound and/or diazonium salt to cause color development.
In the heat-sensitive recording material of the present invention, since all of the heat-sensitive recording layer that color-develops to yellow color (yellow heat-sensitive recording layer), the heat-sensitive recording layer that color-develops to cyan color (cyan heat-sensitive recording layer) and the heat-sensitive recording layer that color-develops to magenta color (magenta heat-sensitive recording layer) are constituted of a layer composed of a diazo compound or the like and a coupler, a decrease in thickness of all the color-development layers and a decrease in thickness of the full-color heat-sensitive recording material itself are possible, and color development of an image can be enhanced. Further, since a diazo compound and a coupler are emulsion-dispersed in a heat-sensitive recording layer or capsulated in microcapsules, curl of a full-color heat-sensitive recording material due to phase transition of contents can be decreased, and handling property can be improved. Further, since the reaction of a diazo compound or the like with a coupler is an irreversible reaction, the stability of an image is further improved as compared with the case of use of an electron-donating colorless dye and the like.
Since the full-color heat-sensitive recording material of the present invention has a structure in which a yellow heat-sensitive recording layer, a cyan heat-sensitive recording layer and a magenta heat-sensitive recording layer are provided in this order from the support side, decrease in the transmittance of light necessary for light-fixation of a diazo compound or the like due to the influence of yellow can be suppressed, and image fixing speed can be improved.
First, the layer constitution of the full-color heat-sensitive recording material of the present invention is described. The full-color heat-sensitive recording material of the present invention is a diazo color-developing system which has a layer structure in which a yellow heat-sensitive recording layer, a cyan heat-sensitive recording layer and a magenta heat-sensitive recording layer are placed in this order from the support side, and in which the color-developing mechanism of each layer is composed of a diazo compound or the like, and a coupler. Specifically, suitable is for example a constitution including a heat-sensitive recording layer containing a diazo compound or the like having a maximum absorption wavelength of 350 nm or less and a coupler reacting with the diazo compound or the like to cause development of yellow color, a light-fixation type heat-sensitive recording layer containing a diazo compound or the like having a maximum absorption wavelength of 370xc2x130 nm and a coupler reacting with the diazo compound or the like to cause development of cyan color, and a light-fixation type heat-sensitive recording layer containing a diazonium salt compound having a maximum absorption wavelength of 430xc2x130 nm and a coupler reacting with the diazonium salt compound to cause development of magenta color, from the support side. In the above-mentioned constitution, the heat-sensitive recording layer that color-develops to yellow color can be used in non-fixation mode, and further improvement of image stability may be performed by using this yellow heat-sensitive recording layer as a light-fixation type heat-sensitive recording layer.
In the heat-sensitive recording material of the present invention, it is preferable to provide a light transmittance-controlling layer and an outermost protective layer on a heat-sensitive recording layer, particularly, a magenta heat-sensitive recording material, and particularly, it is preferable to provide a light transmittance-controlling layer having a constitution in which light transmittance in the wavelength range of light used for light-fixation decreases after fixation, between the light-fixation type magenta heat-sensitive recording layer and the protective layer. In the case of such as heat-sensitive recording material, it is preferable that the light transmittance after the above-mentioned fixation and light irradiation is 10% or less at 350 nm. In this case, the light irradiation means irradiation with light of 13 kJ/m2 at a wavelength of 420 nm conducted by a xenon lamp compulsive tester. Specifically, it means light irradiation at 0.9 W/m2 for 4.0 hours by Weather O meter Ci65 (trade name: manufactured by Atlas Electric Co.).
As the color development component composed of a diazo compound or the like and a coupler contained in each heat-sensitive recording layer in the present invention, those conventionally known can be used. This heat-sensitive recording material may contain a basic substance, sensitizer and the like promoting the reaction of a diazo compound or the like with a coupler. As described above, in the heat-sensitive recording material of the present invention, a known diazo compound or the like and a coupler can be used in combination appropriately. However, for sufficient manifestation of the effect of the present invention, there are combinations of diazo compounds and the like with couplers suitable for a yellow heat-sensitive recording layer, a cyan heat-sensitive recording layer and a magenta heat-sensitive recording layer, and optimum examples of these color development components and combinations thereof are described below.
Heat-sensitive Recording Layer
Yellow Heat-sensitive Recording Layer
A maximum absorption wavelength xcexmax of a diazo compound or the like used in a yellow heat-sensitive recording layer is preferably 350 nm or less, more preferably 340 nm or less from the standpoint of its effect. If a diazo compound or the like has xcexmax at a longer wavelength than the above-mentioned wavelength range, the diazo compound or the like in a yellow heat-sensitive recording layer may be deactivated in some cases by light irradiation in fixing an upper layer.
As the diazo compound or the like in a yellow heat-sensitive recording layer placed at a position nearest to a support in the heat-sensitive recording material of the present invention, a diazo compound of the following general formula (I) is preferable:
General Formula (I) 
In the general formula (I), R1, R2, R3 and R4 each independently represent any group selected from the group consisting of a hydrogen atom, halogen atoms, alkyl groups, aryl groups, xe2x80x94OR51, xe2x80x94SR51, xe2x80x94COOR51, xe2x80x94CONR51R52, xe2x80x94SO2R51, xe2x80x94SO2NR51R52, xe2x80x94COR51, xe2x80x94NR51R52, nitro group and cyano group. R51 and R52 each independently represent any group selected from the group consisting of a hydrogen atom, alkyl groups, aryl groups and acyl group. R5 represents any group selected from the group consisting of a hydrogen atom, alkyl groups, aryl groups, xe2x80x94COOR53, xe2x80x94CONR53R54, xe2x80x94SO2R53, xe2x80x94SO2NR53R54 and xe2x80x94COR53. R53 and R54 each independently represent any group selected from the group consisting of a hydrogen atom, alkyl groups, aryl groups and acyl group.
In the above-mentioned general formula (I), R1, R2, R3 and R4 each independently represent any group selected from the group consisting of a hydrogen atom, halogen atoms, alkyl groups, aryl groups, xe2x80x94OR51, xe2x80x94SR51, xe2x80x94COOR51, xe2x80x94CONR51R52, xe2x80x94SO2R51, xe2x80x94SO2NR51R52, xe2x80x94COR51, xe2x80x94NR51R52, nitro group and cyano group.
In the general formula (I), the halogen atom represented by R1 and R4 is preferably fluorine, chlorine, bromine or iodine, and of them, fluorine and chlorine are preferable.
In the general formula (I), when R1 and R4 represent an alkyl group, unsubstituted alkyl groups and alkyl groups having a substituent are included, and the alkyl group may be linear or branched, and may have an unsaturated bond.
In the general formula (I), the alkyl group represented by R1 and R4 is preferably an alkyl group having 1 to 20 carbon atoms, more preferably an alkyl group having 1 to 10 carbon atoms. Specifically, methyl, ethyl, n-propyl, i-propyl, n-butyl, t-butyl, n-hexyl, n-octyl, 2-ethylhexyl, 3,5,5-trimethylhexyl, dodecyl, 2-chloroethyl, 2-methanesulfonylethyl, 2-methoxyethyl, 2-benzoyloxyethyl, N,N-dibutylcarbamoylmethyl, 2-ethoxycarbonylethyl, butoxycarbonylmethyl, 2-isopropyloxyethyl, 2-(2,5-di-t-amylphenoxy)ethyl, 2-phenoxyethyl, 1-(4-methoxyphenoxy)-2-propyl, 1-(2,5-di-t-amylphenoxy)-2-propyl, benzyl, xcex1-methylbenzyl, trichloromethyl, trifluoromethyl, 2,2,2-trifluoroethyl and the like are preferable.
In the general formula (I), when R1 and R4 represent an aryl group, unsubstituted aryl groups and aryl groups having a substituent are included. As the aryl group represented by R1 and R4, aryl groups having 6 to 30 carbon atoms are preferable. Specifically, phenyl, 4-methylphenyl, 2-chlorophenyl and the like are preferable.
In the general formula (I), when R1and R4 represent xe2x80x94OR51, xe2x80x94SR51, xe2x80x94COOR51, xe2x80x94CONR51R52, xe2x80x94SO2R51, xe2x80x94SO2NR51R52, xe2x80x94COR51 or xe2x80x94NR51R52, R52 and R52 each independently represent any group selected from the group consisting of a hydrogen atom, alkyl groups, aryl groups and acyl group.
In the general formula (I), the alkyl group represented by R51 and R52 includes unsubstituted alkyl groups and alkyl groups having a substituent. As the alkyl group represented by R51 and R52, alkyl groups having 1 to 30 carbon atoms are preferable, and alkyl groups having 1 to 10 carbon atoms are more preferable. Specifically, methyl, ethyl, i-propyl, s-butyl, t-butyl, t-amyl and the like are preferable.
In the general formula (I), the aryl group represented by R51 and R52 includes unsubstituted aryl groups and aryl groups having a substituent. As the aryl group represented by R51 and R52, aryl groups having 6 to 30 carbon atoms are preferable. Specifically, phenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 2-chlorophenyl, 2,5-t-amylphenyl and the like are preferable.
In the general formula (I), the acyl group represented by R51 and R52 includes unsubstituted acyl groups and acyl groups having a substituent. As the acyl group represented by R51 and R52, acyl groups having 1 to 30 carbon atoms are preferable, acyl groups having 1 to 10 carbon atoms are more preferable. Specifically, acetyl, propanoyl, butanoyl, benzonoyl and the like are preferable.
In the general formula (I), R5 represents any group selected from the group consisting of a hydrogen atom, alkyl groups, aryl groups, xe2x80x94COOR53, xe2x80x94CONR53R54, xe2x80x94SO2R53xe2x80x94SO2NR53R54 and xe2x80x94COR53.
In the general formula (I), the alkyl group represented by R5 include unsubstituted alkyl groups and alkyl groups having a substituent, and the alkyl group may be linear or branched, and may have an unsaturated bond. As the alkyl group represented by R5, alkyl groups having 1 to 30 carbon atoms are preferable. Specifically, methyl, ethyl, n-propyl, i-propyl, n-butyl, i-butyl, 2-butyl, t-butyl, n-hexyl, n-octyl, 2-ethylhexyl, 3,5,5-trimethylhexyl, dodecyl, 2-chloroethyl, 2-methanesulfonylethyl, 2-methoxyethyl, 2-methoxypropyl, 2-benzoyloxyethyl, N,N-dibutylcarbamoylmethyl, 2-ethoxycarbonylethyl, butoxyxarbonylmethyl, octyloxycarbonylmethyl, cyclohexyl, 2-isopropyloxyethyl, 2-(2,5-di-t-amylphenoxy)ethyl, 2-phenoxyethyl, 1-(4-methoxyphenoxy)-2-propyl, 1-(2,5-di-t-amylphenoxy)-2-propyl, benzyl, xcex1-methylbenzyl, phenetyl, 3-phenylpropyl, allyl, methallyl, trichloromethyl, trifluoromethyl, 2,2,2-trifluoroethyl and the like are preferable.
In the general formula (I), when R5 represents an aryl group, unsubstituted aryl groups and aryl groups having a substituent are included. As the aryl group represented by R5, aryl groups having 6 to 30 carbon atoms are preferable. Specifically, phenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 4-ethylphenyl, 4-isopropylphenyl and the like are preferable.
In the general formula (I), when R5 represents xe2x80x94COOR53, xe2x80x94CONR53R54, SO2R53, xe2x80x94SO2NR53R54 or COR53, R53 and R54 each independently represent any group selected from the group consisting of a hydrogen atom, alkyl groups, aryl groups and acyl group.
In the general formula (I), the alkyl group represented by R53 and R54 includes unsubstituted alkyl groups and alkyl groups having a substituent. As the alkyl group represented by R53 and R54, alkyl groups having 1 to 30 carbon atoms are preferable, and alkyl groups having 1 to 10 carbon atoms are more preferable. Specifically, methyl, ethyl, i-propyl, s-butyl, t-butyl, t-amyl and the like are preferable.
In the general formula (I), the aryl group represented by R53 and R54 includes unsubstituted aryl groups and aryl groups having a substituent. As the aryl group represented by R53 and R54, aryl groups having 6 to 30 carbon atoms are preferable. Specifically, phenyl, 2-methylphenyl, 3-methylphenyl, 4-methylphenyl, 2-chlorophenyl, 2,5-t-amylphenyl and the like are preferable.
In the general formula (I), the acyl group represented by R53 and R14 includes unsubstituted acyl groups and acyl groups having a substituent. As the acyl group represented by R51 and R52, acyl groups having 1 to 30 carbon atoms are preferable, acyl groups having 1 to 10 carbon atoms are more preferable. Specifically, acetyl, propanoyl, butanoyl, benzonoyl and the like are preferable.
As the specific examples of the diazo compound of the above-described general formula (I), specific examples 1 to 28 are listed below including exemplary compounds (A-1 to A-42) and combination of substituents R1 to R5 in the general formula (I), and the diazo compound used in a yellow heat-sensitive recording layer is not limited to the following compounds. 
The above-mentioned yellow heat-sensitive recording layer may advantageously contain at least one diazo compound of the above-mentioned general formula (I), and two or more compounds may be combined. Further, these compounds may be used together with other diazo compounds. The diazo compound of the above-mentioned general formula (I) is contained in the above-mentioned heat-sensitive recording layer in an amount preferably of 0.02 to 3 g/m2, more preferably of 0.1 to 2 g/m2. When the content is less than 0.02 g/m2, color development is not preferable, and when over 3 g/m2, applied thickness is not preferable.
The compound of the above-mentioned general formula (I) is preferably used together with an aromatic hydrocarbon. As the above-mentioned aromatic hydrocarbon, those having 12 to 50 carbon atoms, preferably 12 to 25 carbon atoms are preferably used from the standpoints of solubility, handling in use form, and the like. As the above-mentioned aromatic hydrocarbon, those of the following general formula (II) are preferable:
General Formula (II) 
In the general formula (II), R40 to R49 each independently represent a hydrogen atom or alkyl group, and n represents an integer of from 0 to 3. R46 and R47, F48 and R49, and R40 and R41 may be mutually connected to form rings. When R40 to R49 represent an alkyl group, the above-mentioned alkyl groups may be linear or branched, and may have an unsaturated bond. Further, substitution positions of R40 to R49 are not particularly restricted.
In the general formula (II), as R46 to R49, a hydrogen atom and alkyl groups having 1 to 9 carbon atoms are preferable and as R40 and R41, a hydrogen atom and a methyl group are preferable. n represents preferably 0 or 1.